Process for producing nodular iron



United States Patent 2,716,604 PROCESS FUR PRDDUCING NDDULAR IRON Harold N. lingart and Robert B. Melrnoth, Detroit, Mich, assignors to Ford Motor Company, Dear-horn, Mich, a corporation of Delaware No Drawing. Application June 15, 1951, Serial No. 231,896

Claims. (Cl. 75-130) This invention is concerned with the founding industry and more particularly with a method for improving the physical properties of nodular cast iron. This so-called nodular iron has received recent widespread publicity both in the current and patent literature and it is thought to be unnecessary to describe it further other than to state that it may be produced by adding sufiicient magnesium or other alkaline earth or alkaline metal to an appropriate gray iron melt to produce a residual of about 0.05 and inoculating the melt just prior to pouring into the mold with any of the many commercially available graphitizing inoculants. This treatment, if properly carried out, will result in an as cast product in which the uncombined carbon is present in the form of spherulites or nodules rather than the flaky form which is characteristic of typical gray iron. The matrix may be either ferritic or pearlitic, depending upon the analysis and casting conditions. As is now well understood in the art, the substantial absence of flaky graphite permits the production of castings having a much higher tensile strength and ductility than ordinary gray iron.

The production of nodular iron castings particularly in highly irregular shapes has been impeded by the persistent occurrence of a phenomenon referred to in the industry as cope defects. This name has been applied because of the tendency of this defect to occur at the upper portion of the castings. A casting seriously weakened by these cope defects may present to the eye a perfect surface and also appear radiographically sound.

However, when fractured, the castings will exhibit a large number of inclusions of unknown composition. While the exact composition of these inclusions is un known, it is apparent that a large amount of graphite is included in their makeup. In a fracture, these inclusions are disclosed as planes of discontinuity varying in size from those barely visible to the naked eye up to one quarter of an inch in diameter. These graphite laden planes of discontinuity, of course, seriously weaken the castings.

The inclusions have been found particularly troublesome in the casting of crankshafts for internal combustiori engines inasmuch as they tend to congregate at the juncture of the pin bearing and cheek, which is precisely the location of maximum stress concentration at which fatigue cracks tend to develop.

It has been discovered that this phenomenon of cope defects can be substantially eliminated by the application to the molten metal of any of the many fluxes which have been developed for use with magnesium.

Particularly good results have been obtained with boric acid, borax, fused borax, and alkali metal fluoborates, as well as the fluxes which are based upon the double chloride of an alkali metal and magnesium. For a detailed description of commercially available fluxes, reference is made to the Metals Handbook, 1948 edition, page 974.

27,716,604 Patented Aug. 30, 1955 While the inventors have not completely developed the theory underlying their invention, it is their belief that oxidizing gasses preferentially oxidize the magnesium content of the magnesium containing iron and that the resultant highly refractory magnesium oxide is responsible for the occurrence of cope defects.

To eliminate these cope defects, the inventors have intimately contacted the magnesium type of flux with the molten magnesium containing iron.

It has been suggested that the magnesium containing alloy be added to the molten iron in the ladle and that a magnesium type flux be added to the ladle to produce a workable slag from the oxidation products of the magnesium containing alloy. In the absence of such a magnesium type flux the magnesium oxide obtained from the oxidation of the magnesium alloy will result in a pasty and unworkable slag which is difficult to exclude from the final molds and which adheres badly to the ladle. The slag on the ladle serves to protect the magnesium content of the iron from oxidation while it is in the ladle. However, it has been found that in pouring the metal from the ladle to the individual molds, sufficient oxidation of the bare metal takes place to induce the formation of a substantial amount of cope defects. It has further been found that this cope defect may be substantially eliminated if granular magnesium type flux is sprinkled on the molten metal stream as it flows from the ladle into the mold. The following are cited as typical commercial heats of nodular iron in which magnesium type flux was dusted on the metal stream while pouring from the ladle to the mold.

HEAT NO. 30898 7100 pounds of cupola iron, 12 pounds of high carbon ferromanganese. Treated in the ladle with 157 pounds of /2" x down and 158 pounds of l Va" 9% magnesiurn-ferro-silicon inoculant, 38 pounds of ferrosilicon. Bath tapping temperature 2760 Fahrenheit. Pouring temperatures: first mold 2530 F, last mold 2440" F., 3 ounces of granular magnesium type flux dusted on metal stream for each mold poured. Fortyeight BA-6303 crankshafts were cast.

Chemical analysis Per cent Carbon -s 3.48 Manganese 0.75 Chromium 0.04 Phosphorus 0.09 Sulphur 0.012 Silicon 2.30 Copper 0.46 Magnesium 0.052

HEAT 30906 7180 pounds of cupola iron, ten pounds of high carbon ferro-manganese, ten pounds of coke. Treated in the ladle with 315 pounds of 9% magnesium-ferro-silicon. Inoculated in the ladle with 30 pounds of 75% ferro-silicon. The bath tapping temperature was 2760 F. Pouring temperature, 2760 F. Pouring temperature into first mold 2500 F. Last mold 2370" F. Cast forty-eight Bi l-6303 crankshafts in conventional sand mold. Two SBA-6303 and 29N 6303 crankshafts in shell molds. SBA shell mold had one flux impregnated strainer in bottom of sprue, /4 of an ounce of flux was sprinkled on metal stream while pouring each shell mold. Three ounces of magnesium type tlux per mold dusted on metal stream while pouring conventional sand molds.

3 Chemical analysis Per cent Carbon 3.56 Manganese 0.63 Chromium Trace Phosphorus 0.10 Sulphur a 0.011 Silicon 2.14 Copper 0.40 Magnesium 0.050

Per cent Potassium chloride 55 Magnesium chloride 34 Calcium fluoride 2 Barium chloride 9 This flux may be manually dusted upon the stream or it may be applied by any of the conventional dry feeding mechanisms commercially available. results may be attained if the granular magnesium type flux be aspirated against the molten stream by a stream of compressed inert gas. When the flux is so applied, the inert gas serves as a blanket to additionally protect the metal from oxidation. Nitrogen is the most practicable inert gas from an economic standpoint, although helium, hydrogen, argon or methane may be substituted if available. The fiux may also be applied in the molten form as by pouring a stream of the magnesium type flux upon the metal stream just as it emerges from the cover of the flux floating on the ladle.

Without regard to the precise manner in which the flux is applied, a small amount of metallic magnesium may be emulsified with the flux to prevent the loss of mag- More advantageous 5 nesium during the transfer from What is claimed'is:

l. The process of producing cast iron castings having free carbon in the nodular form comprising applying a magnesium type flux to the stream of molten iron containing a nodularizing residual of magnesium as the molten iron is poured into the final mold.

2. The process of producing cast iron castings having free carbon in the nodular form comprising preparing a molten iron bath containing a nodularizing residual content of an alkaline earth metal or magnesium, pouring the molten iron into molds and applying to the molten stream a magnesium type flux as said stream flows into the final mold.

3. The process of producing cast iron castings having free carbon in the nodular form comprising preparing a body of molten iron containing a nodularizing residual of magnesium and pouring a magnesium type flux upon the stream of molten iron as it flows into the final mold.

4. The process of producing cast iron castings having free carbon in the nodular form comprising preparing a body of molten iron containinga nodularizing residual of magnesium and pouring a molten magnesium type flux upon the stream of molten metal asit flows into the the ladle to the mold.

1 final mold, said magnesium type flux containing an appreciable amount of molten magnesium to inhibit the loss of magnesium from the molten iron.

5. The process of producing'cast iron castings having free carbon in the modular form comprising preparing a body of molten iron containing a nodularizing residual of magnesium and dusting a granular magnesium type flux upon the stream of molten iron as:it flows into the final mold.

References Cited'in the file of this patent UNITED" STATES PATENTS OTHER REFERENCES American Foundryman, August 1949, page40. 

1. THE PROCESS OF PRODUCING CAST IRON CASTINGS HAVING FREE CARBON IN THE NODULAR FORM COMPRISING APPLYING A MAGNESIUM TYPE FLUX TO THE STREAM OF MOLTEN IRON CONTAINING A NODULARIZING RESIDUAL OF MAGNESIUM AS THE MOLTEN IRON IS POURED INTO THE FINAL MOLD. 